DIY Doctor UK DIY Forums

I hope someone can offer advice with an underfloor heating problem we’re having. The UFH was already in place when we bought the house and the former owner has lost contact with the people who installed it.

We have radiators throughout the house and then two zones of UFH in the kitchen and dining room, both with their own Honeywell thermostat. There is then a third thermostat in the hallway which controls the main central heating system. We have one control panel/timer upstairs next to the hotwater tank.

The problem I’m having is that whenever either of the UFH thermostats call for heating, it also seems to switch on the central heating system for all the radiators. This means that even if the rest of the house is hot, the radiators stay on if the UFH needs to be on (which is often the case as the UFH is much slower to warm up).

I’m trying to understand what the options are so that I can then call an engineer out. Does anyone know if it’s normal for the UFH to require the main central heating system to be running, and are there any ways to “fix” this?
Cheers H

Hi hornet4000,
Somewhere in your system you should be able to find zone valves or mid position valves. The number and types will depend on how the system was designed.
You will need to find a heating engineer who is able to trace and diagnose the problem, it will undoubtedly be very expensive.
Regards S

A TRV is a zone valve, so even when the boiler runs, if the TRV is closed the radiator will not get warm, however a standard TRV is marked *123456 which is about as much use as a chocolate fire guard.

The problem is the bellows or wax type of TRV head have a massive range, so set to say 3 will start to close at 18 degs C but not fully close unto 21 degs C, and the lock shield valve needs setting, as the TRV takes time to open and close, and unless the lock shield valve is throttled back enough the radiator heats up before the TRV can close, so theory the lock shield is set with a differential thermometer, I have one some where, but most people don't and trial and error does not work with two variables.

Answer is to swap the TRV head for an electronic one, [attachment=0]61dmtMm13BL.jpg[/attachment] these have the temperature in degs C or can be set to F, so you have one device you know how it is set, so when only setting the lock shield now much easier, if room over heats close it a tad, head shown cost me £15 each in 2019, they are not linked, as well as the eQ-3 shown, there is also the Terrier i30, mine are bluetooth, which makes them easier to problem, but unless two radiators in one room not really required, the pair of batteries last nearly 2 years, but I change them every year, good quality of course, don't want them to leak.

Since these are programmable you can set each room independently, they will of course only work when the boiler is running, but I have set the eco and comfort settings so a single press of one button toggles between them.

It would not matter if boiler does run, radiators will only heat up when required, the old zone valve for a batch of radiators seems pointless when all radiators can be individually controlled.